The invention relates to an electron-beam device comprising in an evacuated envelope a target onto which at least one electron beam is focussed and a semiconductor emitter device for generating the electron beam. The semiconductor emitter device comprises a semiconductor body with a major surface which carries a first electrically insulating layer having at least one aperture, which semiconductor body comprises a pn-junction. In the semiconductor body, electrons can be generated by means of avalanche multiplication by applying a reverse voltage across the pn-junction. The electrons emanate from the semiconductor body at the location of the aperture in the first electrically insulating layer to form the electron beam. The first insulating layer carries an accellerating electrode which is situated at the edge of the aperture, and which is at least partly covered with a second electrically insulating layer which leaves the aperture in the first insulating layer exposed and which carries electrodes for influencing the electron beam.
The invention also relates to an electron-beam device comprising in an evacuated envelope a target onto which at least one electron beam is focussed and a semiconductor emitter device for generating this electron beam. The semiconductor emitter device comprise a semiconductor body having at a major surface a p-type surface zone, which zone has at least two connections. At least one of the connections is an injecting connection whose distance from the major surface is at most equal to the diffusion-recombination length of electrons in the p-type surface zone. The major surface is covered at least partly, with an electrically insulating layer formed with an aperture which leaves at least a part of the p-type surface zone exposed and which carries electrodes for influencing the electron beam.
The invention relates in addition to a semiconductor emitter device for use in such an electron-beam device.
Such devices are known from Netherlands Patent Application No. 8,104,893 (corresponding to U.S. Pat. No. 4,574,216) which is laid open to public inspection and is considered to be incorporated herein by reference.
The electron-beam device may be a television camera-tube. In this case the target is a photosensitive layer. However, the electron-beam device may also be a cathode-ray tube for displaying monochrome or coloured images. In that case, the target is a layer or a pattern of lines or dots of fluorescent material (phosphor). The electron-beam device may, however, also be designed for electron lithographic or electron microscopic uses.
Netherlands Patent Application No. 7,905,470 (corresponding to U.S. Pat. No. 4,303,930) which is laid open to public inspection and is considered to be incorporated herein by reference, illustrates a cathode-ray tube comprising a semiconductor emitter device, a so-called "cold cathode". The operation of this cold cathode is based on the emanation of electrons from a semiconductor body in which a pn-junction is reverse-biased in such a way that avalanche multiplication of charge carriers occurs. Some electrons may then obtain so much kinetic energy as is necessary to surpass the electron work function. These electrons are then released at the major surface of the semiconductor emitter body and hence, provide an electron current.
Emanation of electrons is facilitated in the device shown by providing the semiconductor device with accelerating electrodes on an insulating layer which is situated on the major surface, which accelerating electrodes leave exposed an annular, circular, slot-shaped or rectangular aperture in the insulating layer. In order to further facilitate the emanation of electrons, the semiconductor surface is provided, if desired, with an electron work function-reducing material, for example cesium.
Netherlands Patent Application No. 7,800,987 (corresponding to U.S. Pat. No. 4,259,678), which is laid open to public inspection and is considered to be incorporated herein by reference, discloses a similar type of "cold cathode" in which the pn-junction is left, exposed at the major surface of the semiconductor body.
As a certain amount of residual gases inevitably remains in the evacuated envelope, negative and positive ions are liberated from these residual gases by the electron current. The negative ions are accelerated in the direction of the target. In the case of electrostatic deflection, they may be incident on a small area of the target and either damage or disturb its operation. Under the influence of accelerating and focussing fields in the tube, some of the positive ions will move in the direction of the cathode. If no special measures are taken, some of the positive ions will be incident on the semiconductor and a kind of ion-etching will take place causing damage to the semiconductor. This damage may be a gradual etching away of the electron work function-reducing material. A redistribution or even total disappearance of this material causes the emission properties of the cathode to change. If there is no such layer (or if it has been removed by the above-mentioned etching mechanism), even the major surface of the semiconductor body may be effected. A solution of this problem is provided by the above-mentioned Netherlans Patent Application No. 8,104,893, which is considered to be incorporated herein by reference. Due to the use of an additional electrically insulating layer on which at least two deflection electrodes for generating a dipole field are present, the positive ions are made to follow such a path that they do not, or hardly, impinge on the emissive part of the cathode. The electron beam is deflected by the dipole field, In the field of electron optics, there is an increasing need for a qualitatively suitable electron-beam focus on the target, i.e. a focus having the required shape and dimensions and without a halo around it.